I have a Liebherr fridge / freezer model KGNV 3846. The temp in the freezer goes up and down, anything from -3 to -15. The freezer also gets filled up with ice pretty easily. The fan isn’t working in the freezer as it’s blocked with ice and I wanted to check that this was the most likely reason for the problems with the temperature. Should defrosting the freezer clear this and approx how long should this take. The alternative is to open the back panel of the freezer and manually remove the ice from the fan but nit sure what tool I would need or if I should be doing it myself.